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We show that an acoustic crystalline wave gives rise to an effect similar to that of a gravitational wave to an electron gas. Applying this idea to a two-dimensional electron gas in the fractional quantum Hall regime, this allows for experimental study of its intra-Landau level dynamical response in the long-wavelength limit. To study such response we generalize Haldane's geometrical description of fractional quantum Hall states to situations where the external metric is time dependent. We... Show moreWe show that an acoustic crystalline wave gives rise to an effect similar to that of a gravitational wave to an electron gas. Applying this idea to a two-dimensional electron gas in the fractional quantum Hall regime, this allows for experimental study of its intra-Landau level dynamical response in the long-wavelength limit. To study such response we generalize Haldane's geometrical description of fractional quantum Hall states to situations where the external metric is time dependent. We show that such time-dependent metric (generated by acoustic wave) couples to collective modes of the system, including a quadrapolar mode at long wavelength, and magnetoroton at finite wavelength. Energies of these modes can be revealed in spectroscopic measurements, controlled by strain-induced Fermi velocity anisotropy. We argue that such geometrical probe provides a potentially highly useful alternative probe of quantum Hall liquids, in addition to the usual electromagnetic response. Show less

Pump-probe optical spectroscopy was used to investigate proposed charge-carrier multiplication via impact ionization in the M-1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed a larger ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple time scales within the charge dynamics and... Show morePump-probe optical spectroscopy was used to investigate proposed charge-carrier multiplication via impact ionization in the M-1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed a larger ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple time scales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that a fast carrier multiplication process, i.e., impact ionization, acts efficiently in this prototypical strongly correlated insulator, as was recently predicted by theoretical calculations. Show less

Date Issued

2016-10-17

Identifier

FSU_libsubv1_wos_000386097100004, 10.1103/PhysRevB.94.155129

Format

Citation

Title

Equilibrium, metastability, and hysteresis in a model spin-crossover material with nearest-neighbor antiferromagnetic-like and long-range ferromagnetic-like interactions.

Phase diagrams and hysteresis loops were obtained by Monte Carlo simulations and a mean- field method for a simplified model of a spin-crossovermaterialwith a two-step transition between the high-spin and low-spin states. This model is a mapping onto a square-lattice S = 1/2 Ising model with antiferromagnetic nearest-neighbor and ferromagnetic Husimi-Temperley ( equivalent-neighbor) long-range interactions. Phase diagrams obtained by the two methods for weak and strong long-range interactions... Show morePhase diagrams and hysteresis loops were obtained by Monte Carlo simulations and a mean- field method for a simplified model of a spin-crossovermaterialwith a two-step transition between the high-spin and low-spin states. This model is a mapping onto a square-lattice S = 1/2 Ising model with antiferromagnetic nearest-neighbor and ferromagnetic Husimi-Temperley ( equivalent-neighbor) long-range interactions. Phase diagrams obtained by the two methods for weak and strong long-range interactions are found to be similar. However, for intermediate-strength long-range interactions, the Monte Carlo simulations show that tricritical points decompose into pairs of critical end points and mean-field critical points surrounded by horn-shaped regions of metastability. Hysteresis loops along paths traversing the horn regions are strongly reminiscent of thermal two-step transition loops with hysteresis, recently observed experimentally in several spin-crossover materials. We believe analogous phenomena should be observable in experiments and simulations for many systems that exhibit competition between local antiferromagnetic-like interactions and long-range ferromagnetic-like interactions caused by elastic distortions. Show less

The multilevel system Mn-55(2 vertical bar) is used to generate two pseudoharmonic level systems, as representations of the same electronic sextuplet at different nuclear spin projections. The systems are coupled using a forbidden nuclear transition induced by the crystalline anisotropy. We demonstrate Rabi oscillations between the two representations in conditions similar to two coupled pseudoharmonic quantum oscillators. Rabi oscillations are performed at a detuned pumping frequency which... Show moreThe multilevel system Mn-55(2 vertical bar) is used to generate two pseudoharmonic level systems, as representations of the same electronic sextuplet at different nuclear spin projections. The systems are coupled using a forbidden nuclear transition induced by the crystalline anisotropy. We demonstrate Rabi oscillations between the two representations in conditions similar to two coupled pseudoharmonic quantum oscillators. Rabi oscillations are performed at a detuned pumping frequency which matches the energy difference between electronuclear states of different oscillators. We measure a coupling stronger than the decoherence rate to indicate the possibility of fast information exchange between the systems. Show less

Hexagonal BaIrO3 is a magnetic insulator driven by the spin-orbit interaction (SOI), whereas BaRuO3 is an enhanced paramagnetic metal. Our investigation of structural, magnetic, transport, and thermal properties reveals that substitution of Ru4+ (4d(4)) ions for Ir4+ (5d(5)) ions in BaIrO3 reduces the magnitudes of the SOI and a monoclinic structural distortion and rebalances the competition between the SOI and the lattice degrees of freedom to render an evolution from a magnetic insulting... Show moreHexagonal BaIrO3 is a magnetic insulator driven by the spin-orbit interaction (SOI), whereas BaRuO3 is an enhanced paramagnetic metal. Our investigation of structural, magnetic, transport, and thermal properties reveals that substitution of Ru4+ (4d(4)) ions for Ir4+ (5d(5)) ions in BaIrO3 reduces the magnitudes of the SOI and a monoclinic structural distortion and rebalances the competition between the SOI and the lattice degrees of freedom to render an evolution from a magnetic insulting state to a robust metallic state. The central findings of this paper are as follows: (1) light Ru doping (0 < x <= 0.15) prompts simultaneous, precipitous drops in both the magnetic ordering temperature T-N and the electrical resistivity, and (2) heavier Ru doping (0.41 <= x <= 0.9) induces a robust metallic state without any long-range magnetic order. All results suggest a critical role of the lattice degrees of freedom in determining the ground state in the heavy transition-metal oxides. Show less

We report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to P = 16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at P similar to 8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative dT(c)/dP observed in a range between P similar to 8 and 12 kbar may be explained by the reduction in the density of states due to the... Show moreWe report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to P = 16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at P similar to 8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative dT(c)/dP observed in a range between P similar to 8 and 12 kbar may be explained by the reduction in the density of states due to the reconstruction. The ratio of the transition temperature to the effective Fermi energy remains high under high pressure: k(B)T(c)/E-F similar to 0.1 even at P = 16.1 kbar. Show less

Date Issued

2016-03-03

Identifier

FSU_libsubv1_wos_000371401700003, 10.1103/PhysRevB.93.094505

Format

Citation

Title

Evidence For Correlated Dynamics Near The Berezinskii-kosterlitz-thouless-like Transition In Highly Underdoped La2-xsrxcuo4.

Creator

Shi, Zhenzhong, Shi, Xiaoyan, Popovic, Dragana

Abstract/Description

A low-frequency resistance noise study in highly underdoped thick films of La2-xSrxCuO4 (x = 0.07 and 0.08) reveals slow, correlated dynamics and breaking of ergodicity near the superconducting transition of the Berezinskii-Kosterlitz-Thouless type. The observed correlated behavior is strongly suppressed by disorder.

Date Issued

2016-10-05

Identifier

FSU_libsubv1_wos_000385239900002, 10.1103/PhysRevB.94.134503

Format

Citation

Title

Extremely Large Nonsaturating Magnetoresistance And Ultrahigh Mobility Due To Topological Surface States In The Metallic Bi2te3 Topological Insulator.

Creator

Shrestha, K., Chou, M., Graf, D., Yang, H. D., Lorenz, B., Chu, C. W.

Abstract/Description

Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge-carrier concentrations. At low charge-carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge-carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to... Show moreWeak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge-carrier concentrations. At low charge-carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge-carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. The observations of an extremely large nonsaturating magnetoresistance and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. The physical parameters characterizing the WAL effects are calculated using the Hikami-LarkinNagaoka formula. At high charge-carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge-carrier concentrations. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magnetoelectric sensors and memory devices. Show less

On the triangular and kagome lattices, short-ranged resonating valence-bond wave functions can be sampled without the sign problem using a recently developed Pfaffian Monte Carlo scheme. In this Rapid Communication, we study the Renyi entanglement entropy in these wave functions using a replica-trick method. Using various spatial bipartitions, including the Levin-Wen construction, our finite-size scaled Renyi entropy gives a topological contribution consistent with. gamma = ln( 2), as... Show moreOn the triangular and kagome lattices, short-ranged resonating valence-bond wave functions can be sampled without the sign problem using a recently developed Pfaffian Monte Carlo scheme. In this Rapid Communication, we study the Renyi entanglement entropy in these wave functions using a replica-trick method. Using various spatial bipartitions, including the Levin-Wen construction, our finite-size scaled Renyi entropy gives a topological contribution consistent with. gamma = ln( 2), as expected for a gapped Z(2) quantum spin liquid. We prove that the mutual statistics is consistent with the toric code anyon model and rule out any other quasiparticle statistics such as the double semion model. Show less

Date Issued

2017-03-06

Identifier

FSU_libsubv1_wos_000396000700001, 10.1103/PhysRevB.95.100402

Format

Citation

Title

Frustrated Magnetism In The Tetragonal Cose Analog Of Superconducting Fese.

Recently synthesized metastable tetragonal CoSe, isostructural to the FeSe superconductor, offers a new avenue for investigating systems in close proximity to the iron-based superconductors. We present magnetic and transport property measurements on powders and single crystals of CoSe. High field magnetic susceptibility measurements indicate a suppression of the previously reported 10 K ferromagnetic transition with the magnetic susceptibility, exhibiting time dependence below the proposed... Show moreRecently synthesized metastable tetragonal CoSe, isostructural to the FeSe superconductor, offers a new avenue for investigating systems in close proximity to the iron-based superconductors. We present magnetic and transport property measurements on powders and single crystals of CoSe. High field magnetic susceptibility measurements indicate a suppression of the previously reported 10 K ferromagnetic transition with the magnetic susceptibility, exhibiting time dependence below the proposed transition. Dynamic scaling analysis of the time dependence yields a critical relaxation time of tau* = 0.064 +/- 0.008 s which in turn yields activation energy E-a(*) = 14.84 +/- 0.59 K and an ideal glass temperature T-0(*) = 8.91 +/- 0.09 K from Vogel-Fulcher analysis. No transition is observed in resistivity and specific heat measurements, but both measurements indicate that CoSe is metallic. These results are interpreted on the basis of CoSe exhibiting frustrated magnetic ordering arising from competing magnetic interactions. Arrott analysis of single crystal magnetic susceptibility has indicated the transition temperature occurs in close proximity to previous reports and that the magnetic moment lies solely in the ab plane. The results have implications for understanding the relationship between magnetism and transport properties in the iron chalcogenide superconductors. Show less

We develop a variational scheme called the "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method exploits the low-entanglement property of the ground state of local Hamiltonians in combination with the framework of the Gutzwiller wave function and indicates that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a... Show moreWe develop a variational scheme called the "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method exploits the low-entanglement property of the ground state of local Hamiltonians in combination with the framework of the Gutzwiller wave function and indicates that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a surprisingly small number of variational parameters. We perform benchmark calculations of the single-band AIM that validate our theory and suggest that the GRG might enable us to study complex systems beyond the reach of the other methods presently available and pave the way to interesting generalizations, e.g., to nonequilibrium transport in nanostructures. Show less

Date Issued

2016-01-06

Identifier

FSU_libsubv1_wos_000367665400002, 10.1103/PhysRevB.93.045103

Format

Citation

Title

Magnetotransport in double quantum well with inverted energy spectrum: HgTe/CdHgTe.

We present an experimental study of the double-quantum-well (DQW) system made of two-dimensional layers with inverted energy band spectrum: HgTe. The magnetotransport reveals a considerably larger overlap of the conduction and valence subbands than in known HgTe single quantum wells (QW), which may be regulated here by an applied gate voltage V-g. This large overlap manifests itself in a much higher critical field B-c separating the range above it with a plain behavior of the Hall... Show moreWe present an experimental study of the double-quantum-well (DQW) system made of two-dimensional layers with inverted energy band spectrum: HgTe. The magnetotransport reveals a considerably larger overlap of the conduction and valence subbands than in known HgTe single quantum wells (QW), which may be regulated here by an applied gate voltage V-g. This large overlap manifests itself in a much higher critical field B-c separating the range above it with a plain behavior of the Hall magnetoresistance rho(xy) (B), where the quantum peculiarities shift linearly with V-g, and the range below with a complicated behavior. In the latter case, specific structures in rho(xy) (B) are formed like a double-N-shaped rho(xy) (B), reentrant sign-alternating quantum Hall effect with transitions into a zero-filling-factor state, etc., which are clearly manifested here due to better magnetic quantization at high fields, as compared to the features seen earlier in a single HgTe QW. The coexisting electrons and holes were found in the whole investigated range of positive and negative V-g as revealed (i) from fits to the low-field N-shaped rho(xy) (B), (ii) from the Fourier analysis of oscillations in rho(xx) (B), and (iii) from a specific behavior of rho(xy) (B) at high positive V-g. A peculiar feature here is that the found electron density n remains almost constant in the whole range of investigated V-g while the hole density p drops down from the value a factor of 6 larger than n at extreme negative V-g to almost zero at extreme positive V-g passing through the charge-neutrality point. We show that this difference between n and p stems from an order of magnitude larger density of states for holes in the lateral valence subband maxima than for electrons in the conduction subband minimum. We analyze our observations on the basis of a calculated picture of magnetic levels in a DQW and suggest that their specificity is due to (i) a nonmonotonic course of the valence subband magnetic levels and an oscillating behavior of the valence subband top versus field due to lateral maxima in the energy spectrum, (ii) a reduced gap between the lowest-electron and the highest-hole magnetic levels where the electron- and hole-type localized states are superposed, and (iii) a possible formation of the interlayer electron-hole excitons. Show less

Thin Bi2Te3 single crystals laid on Scotch tape are investigated by Fourier transform infrared spectroscopy at 4 K and in a magnetic field up to 35 T. The magnetotransmittance spectra of the Bi2Te3/tape composite are analyzed as a stacked-slab system, and the average thickness of Bi2Te3 is estimated to be 6.4 +/- 1.7 mu m. The optical conductivity of Bi2Te3 at different magnetic fields is then extracted, and we find that the magnetic field modifies the optical conductivity in the following... Show moreThin Bi2Te3 single crystals laid on Scotch tape are investigated by Fourier transform infrared spectroscopy at 4 K and in a magnetic field up to 35 T. The magnetotransmittance spectra of the Bi2Te3/tape composite are analyzed as a stacked-slab system, and the average thickness of Bi2Te3 is estimated to be 6.4 +/- 1.7 mu m. The optical conductivity of Bi2Te3 at different magnetic fields is then extracted, and we find that the magnetic field modifies the optical conductivity in the following ways: (1) Field-induced transfer of the optical weight from the lower-frequency regime (< 250 cm(-1)) to the higher-frequency regime (> 250 cm(-1)) due to the redistribution of charge carriers across the Fermi surface. (2) Evolving of a Fano-resonance-like spectral feature from an antiresonance to a resonance with increasing magnetic field. Such behavior can be attributed to the electron-phonon interactions between the E-u(1) optical phonon mode and the continuum of electronic transitions. (3) Cyclotron resonance resulting from the intervalence band Landau level transitions, which can be described by the electrodynamics of massive Dirac holes. Show less

We combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale alpha-Fe2O3. Analysis of the d-to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in... Show moreWe combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale alpha-Fe2O3. Analysis of the d-to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in alpha-Fe2O3 and other iron-containing nanomaterials that may be useful for advanced sensing applications. We also unravel the size dependence of collective excitations in this iconic antiferromagnet. Show less

We have carried out Cu-63,Cu-65 NMR spectra measurements in a magnetic field up to about 45 T on a single crystal of a multiferroic triangular antiferromagnet CuCrO2. The measurements were performed for magnetic fields aligned along the crystal c axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H less than or similar to 15 T). At higher fields magnetic... Show moreWe have carried out Cu-63,Cu-65 NMR spectra measurements in a magnetic field up to about 45 T on a single crystal of a multiferroic triangular antiferromagnet CuCrO2. The measurements were performed for magnetic fields aligned along the crystal c axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H less than or similar to 15 T). At higher fields magnetic structures form within individual triangular planes whereas the spin directions of the magnetic ions from neighboring planes are not correlated. It is established that the 2D-3D transition is hysteretic in field and temperature. Line-shape analysis reveals several possible magnetic structures existing within individual planes for different phases of CuCrO2. Within certain regions on the magnetic H-T phase diagram of CuCrO2 a 3D magnetic ordering with tensor order parameter is expected. Show less

Date Issued

2016-09-12

Identifier

FSU_libsubv1_wos_000383138700003, 10.1103/PhysRevB.94.094410

Format

Citation

Title

Magnetic Ground States And Magnetodielectric Effect In Rcr(bo3)(2) (r = Y And Ho).

The layered perovskites RCr(BO3)(2) (R = Y and Ho) with magnetic triangular lattices were studied by performing ac/dc susceptibility, specific heat, elastic and inelastic neutron scattering, and dielectric constant measurements. The results show (i) both samples' Cr3+ spins order in a canted antiferromagnetic structure with TN around 8-9 K, while the Ho3+ ions do not order down to T = 1.5 K in HoCr(BO3)(2); (ii) when a critical magnetic field HC around 2-3 T is applied below TN, the Cr3+... Show moreThe layered perovskites RCr(BO3)(2) (R = Y and Ho) with magnetic triangular lattices were studied by performing ac/dc susceptibility, specific heat, elastic and inelastic neutron scattering, and dielectric constant measurements. The results show (i) both samples' Cr3+ spins order in a canted antiferromagnetic structure with TN around 8-9 K, while the Ho3+ ions do not order down to T = 1.5 K in HoCr(BO3)(2); (ii) when a critical magnetic field HC around 2-3 T is applied below TN, the Cr3+ spins in the Y compound and both the Cr3+ and Ho3+ spins in the Ho compound order in a ferromagnetic state; (iii) both samples exhibit dielectric constant anomalies around the transition temperature and critical field, but the Ho compound displays a much stronger magnetodielectric response. We speculate that this is due to the magnetostriction, which depends on both the Cr3+ and the Ho3+ ions' ordering in the Ho compound. Moreover, by using linear spin-wave theory to simulate the inelastic neutron scattering data, we estimated the Y compound's intralayer and interlayer exchange strengths as ferromagnetic J(1) = -0.12 meV and antiferromagnetic J(2) = 0.014 meV, respectively. The competition between different kinds of superexchange interactions results in the ferromagnetic intralayer interaction. Show less

We report interlayer electronic transport in CaMnBi2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. The small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi2, which features an anisotropic Dirac cone, our results suggest that magnetic... Show moreWe report interlayer electronic transport in CaMnBi2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. The small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi2, which features an anisotropic Dirac cone, our results suggest that magnetic-field-induced changes in interlayer conduction are also present in layered bismuth-based materials with a zero-energy line in momentum space created by the staggered alkaline earth atoms. Show less

There has been a growing interest in realizing topologically nontrivial states of matter in band insulators, where a quantum Hall effect can appear as an intrinsic property of the band structure. While ongoing progress is under way with a number of directions, the possibility of realizing novel interaction-generated topological phases, without the requirement of a nontrivial invariant encoded in single-particle wave function or band structure, can significantly extend the class of topological... Show moreThere has been a growing interest in realizing topologically nontrivial states of matter in band insulators, where a quantum Hall effect can appear as an intrinsic property of the band structure. While ongoing progress is under way with a number of directions, the possibility of realizing novel interaction-generated topological phases, without the requirement of a nontrivial invariant encoded in single-particle wave function or band structure, can significantly extend the class of topological materials and is thus of great importance. Here, we show an interaction-driven topological phase emerging in an extended Bose-Hubbard model on a kagome lattice, where the noninteracting band structure is topological trivial with zero Berry curvature in the Brillouin zone. By means of an unbiased state-of-the-art density-matrix renormalization group technique, we identify that the ground state in a broad parameter region is equivalent to a bosonic fractional quantum Hall Laughlin state, based on the characterization of universal properties including ground-state degeneracy, edge excitations, and anyonic quasiparticle statistics. Our work paves a way to finding an interaction-induced topological phase at the phase boundary of conventionally ordered solid phases. Show less

We analyze general zero mode properties of the parent Hamiltonian of the unprojected Jain-2/5 state. We characterize the zero mode condition associated to this Hamiltonian via projection onto a four-dimensional two-particle subspace for given pair angular momentum, for the disk and similarly for the spherical geometry. Earlier numerical claims in the literature about ground-state uniqueness on the sphere are substantiated on analytic grounds, and related results are derived. Preference is... Show moreWe analyze general zero mode properties of the parent Hamiltonian of the unprojected Jain-2/5 state. We characterize the zero mode condition associated to this Hamiltonian via projection onto a four-dimensional two-particle subspace for given pair angular momentum, for the disk and similarly for the spherical geometry. Earlier numerical claims in the literature about ground-state uniqueness on the sphere are substantiated on analytic grounds, and related results are derived. Preference is given to second-quantized methods, where zero mode properties are derived not from given analytic wave functions, but from a "lattice" Hamiltonian and associated zero mode conditions. This method reveals new insights into the guiding-center structure of the unprojected Jain-2/5 state, in particular, a system of dominance patterns following a "generalized Pauli principle," which establishes a complete one-to-one correspondence with the edge mode counting. We also identify one-body operators that function as generators of zero modes. Show less

We present results from point-contact spectroscopy of the antiferromagnetic heavy-fermion superconductor UPd2Al3: Conductance spectra are taken from single crystals with two major surface orientations as a function of temperature andmagnetic field and analyzed using a theory of cotunneling into anAnderson lattice. Spectroscopic signatures are clearly identified, including the distinct asymmetric double-peak structure arising from the opening of a hybridization gap when a coherent heavy-Fermi... Show moreWe present results from point-contact spectroscopy of the antiferromagnetic heavy-fermion superconductor UPd2Al3: Conductance spectra are taken from single crystals with two major surface orientations as a function of temperature andmagnetic field and analyzed using a theory of cotunneling into anAnderson lattice. Spectroscopic signatures are clearly identified, including the distinct asymmetric double-peak structure arising from the opening of a hybridization gap when a coherent heavy-Fermi liquid is formed. Both the hybridization gap, found to be 7.2 +/- 0.3meV at 4 K, and the conductance enhancement above a flat background decrease upon increasing temperature. While the hybridization gap is extrapolated to remain finite up to similar to 28 K, close to the temperature around which the magnetic susceptibility displays a broad peak, the conductance enhancement vanishes at similar to 18 K, slightly above the antiferromagnetic transition temperature (T-N approximate to 14 K). This rapid decrease of the conductance enhancement is understood as a consequence of the junction drifting away from the ballistic regime due to increased scattering off magnons associated with the localized U 5f electrons. This shows that while the hybridization gap opening is not directly associated with the antiferromagnetic ordering, its visibility in the conductance is greatly affected by the temperature-dependent magnetic excitations. Our findings are not only consistent with the 5f dual-nature picture in the literature but also shed new light on the interplay between the itinerant and localized electrons in UPd2Al3. Show less

MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R ... Show moreMnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiO3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought. Show less

We report infrared magnetospectroscopy studies on thin crystals of an emerging Dirac material ZrTe5 near the intrinsic limit. The observed structure of the Landau-level transitions and zero-field infrared absorption indicate a two-dimensional Dirac-like electronic structure, similar to that in graphene but with a small relativistic mass corresponding to a 9.4-meV energy gap. Measurements with circularly polarized light reveal a significant electron-hole asymmetry, which leads to splitting of... Show moreWe report infrared magnetospectroscopy studies on thin crystals of an emerging Dirac material ZrTe5 near the intrinsic limit. The observed structure of the Landau-level transitions and zero-field infrared absorption indicate a two-dimensional Dirac-like electronic structure, similar to that in graphene but with a small relativistic mass corresponding to a 9.4-meV energy gap. Measurements with circularly polarized light reveal a significant electron-hole asymmetry, which leads to splitting of the Landau-level transitions at high magnetic fields. Our model, based on the Bernevig-Hughes-Zhang effective Hamiltonian, quantitatively explains all observed transitions, determining the values of the Fermi velocity, Dirac mass (or gap), electron-hole asymmetry, and electron and hole g factors. Show less

Slow magneto-oscilations of the conductivity are observed in a 75-nm-wide quantum well at heating of the two-dimensional electrons by a high-intensity surface acoustic wave. These magneto-oscillations are caused by intersubband elastic scattering between the symmetric and asymmetric subbands formed due to an electrostatic barrier in the center of the quantum well. The tunneling splitting between these subbands as well as the intersubband scattering rate are determined.

Date Issued

2018-02-20

Identifier

FSU_libsubv1_wos_000425492500009, 10.1103/PhysRevB.97.075427

Format

Citation

Title

Hall Effect Within The Colossal Magnetoresistive Semimetallic State Of Mote2.

Here, we report a systematic study on the Hall effect of the semimetallic state of bulk MoTe2, which was recently claimed to be a candidate for a novel type of Weyl semimetallic state. The temperature (T) dependence of the carrier densities and of their mobilities, as estimated from a numerical analysis based on the isotropic two-carrier model, indicates that its exceedingly large and nonsaturating magnetoresistance may be attributed to a near perfect compensation between the densities of... Show moreHere, we report a systematic study on the Hall effect of the semimetallic state of bulk MoTe2, which was recently claimed to be a candidate for a novel type of Weyl semimetallic state. The temperature (T) dependence of the carrier densities and of their mobilities, as estimated from a numerical analysis based on the isotropic two-carrier model, indicates that its exceedingly large and nonsaturating magnetoresistance may be attributed to a near perfect compensation between the densities of electrons and holes at low temperatures. A sudden increase in hole density, with a concomitant rapid increase in the electron mobility below T similar to 40 K, leads to comparable densities of electrons and holes at low temperatures suggesting a possible electronic phase transition around this temperature. Show less

By using acoustic methods the complex high-frequency conductance of high-mobility n-GaAs/AlGaAs heterostructures was determined in magnetic fields 12-18 T. Based on the observed frequency and temperature dependences, we conclude that in the investigated magnetic field range and at sufficiently low temperatures, T less than or similar to 200 mK, the electron system forms a Wigner crystal deformed due to pinning by disorder. At some temperature, which depends on the electron filling factor, the... Show moreBy using acoustic methods the complex high-frequency conductance of high-mobility n-GaAs/AlGaAs heterostructures was determined in magnetic fields 12-18 T. Based on the observed frequency and temperature dependences, we conclude that in the investigated magnetic field range and at sufficiently low temperatures, T less than or similar to 200 mK, the electron system forms a Wigner crystal deformed due to pinning by disorder. At some temperature, which depends on the electron filling factor, the temperature dependences of both components of the complex conductance get substantially changed. We have ascribed this rapid change of the conduction mechanism to melting of the Wigner crystal and study the dependence of the so-defined melting temperature on the electron filling factor. Show less

Date Issued

2016-08-15

Identifier

FSU_libsubv1_wos_000381482600007, 10.1103/PhysRevB.94.075420

Format

Citation

Title

Non-ising-like Two-dimensional Superconductivity In A Bulk Single Crystal.

Creator

Zhang, Q. R., Rhodes, D., Zeng, B., Johannes, M. D., Balicas, L.

Abstract/Description

Both Nb3PdxSe7 and Ta4Pd3Te16 crystallize in a monoclinic point group while exhibiting superconducting transition temperatures as high as T-c similar to 3.5 and similar to 4.7K, respectively. Disorder was claimed to lead to the extremely large upper critical fields (H-c2) observed in related compounds. Despite the presence of disorder and heavier elements, H-c2s in Ta4Pd3Te16 are found to be considerably smaller than those of Nb3PdxSe7 while displaying an anomalous, nonsaturating linear... Show moreBoth Nb3PdxSe7 and Ta4Pd3Te16 crystallize in a monoclinic point group while exhibiting superconducting transition temperatures as high as T-c similar to 3.5 and similar to 4.7K, respectively. Disorder was claimed to lead to the extremely large upper critical fields (H-c2) observed in related compounds. Despite the presence of disorder and heavier elements, H-c2s in Ta4Pd3Te16 are found to be considerably smaller than those of Nb3PdxSe7 while displaying an anomalous, nonsaturating linear dependence on temperature T for fields along all three crystallographic axes. In contrast, crystals of the latter compound displaying the highest T(c)s display H-c2 alpha (1-T/T-c)(1/2), which in monolayers of transition metal dichalcogenides is claimed to be evidence for an Ising paired superconducting state resulting from strong spin-orbit coupling. This anomalous T dependence indicates that the superconducting state of Nb3PdxSe7 is quasi-two-dimensional in nature. This is further supported by a nearly divergent anisotropy in upper-critical fields, i.e., gamma= H-c2(b)/H-c2(a)', upon approaching T-c. Hence, in Nb3PdxSe7 the increase of T-c correlates with a marked reduction in electronic dimensionality as observed, for example, in intercalated FeSe. For the Nb compound, Density functional theory (DFT) calculations indicate that an increase in the external field produces an anisotropic orbital response, with especially strong polarization at the Pd sites when the field is perpendicular to their square planar environment. The field also produces an anisotropic spin moment at both Pd sites. Therefore, DFT suggests the field-induced pinning of the spin to the lattice as a possible mechanism for decoupling the superconducting planes. Show less

Date Issued

2016-09-12

Identifier

FSU_libsubv1_wos_000383138700005, 10.1103/PhysRevB.94.094511

Format

Citation

Title

Multiple Crossovers And Coherent States In A Mott-peierls Insulator.

Creator

Najera, O., Civelli, M., Dobrosavljevic, V., Rozenberg, M. J.

Abstract/Description

We consider the dimer Hubbard model within dynamical mean-field theory to study the interplay and competition between Mott and Peierls physics. We describe the various metal-insulator transition lines of the phase diagram and the breakdown of the different solutions that occur along them. We focus on the specific issue of the debated Mott-Peierls insulator crossover and describe the systematic evolution of the electronic structure across the phase diagram. We found that at low intradimer... Show moreWe consider the dimer Hubbard model within dynamical mean-field theory to study the interplay and competition between Mott and Peierls physics. We describe the various metal-insulator transition lines of the phase diagram and the breakdown of the different solutions that occur along them. We focus on the specific issue of the debated Mott-Peierls insulator crossover and describe the systematic evolution of the electronic structure across the phase diagram. We found that at low intradimer hopping, the emerging local magnetic moments can unbind above a characteristic singlet temperature T*. Upon increasing the interdimer hopping, subtle changes occur in the electronic structure. Notably, we find Hubbard bands of a mix character with coherent and incoherent excitations. We argue that this statemight be relevant formaterials such as VO2 and its signaturesmay be observed in spectroscopic studies, and possibly through pump-probe experiments. Show less

The magnetoelectronic properties of La1-xSrxCoO3, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at x(C) similar to 0.18. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used La-139 nuclear magnetic resonance to... Show moreThe magnetoelectronic properties of La1-xSrxCoO3, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at x(C) similar to 0.18. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used La-139 nuclear magnetic resonance to investigate the transition from hopping dynamics for x < x(C) to Korringa-like ferromagnetic metal behavior for x > x(C). A marked decrease in the spin-lattice relaxation rate is found in the vicinity of x(C) as the MI transition is crossed. This behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size. Show less

Date Issued

2016-01-25

Identifier

FSU_libsubv1_wos_000369218500003, 10.1103/PhysRevB.93.024204

Format

Citation

Title

Coexistence of Weyl physics and planar defects in the semimetals TaP and TaAs.

We report a structural study of the Weyl semimetals TaAs and TaP, utilizing diffraction and imaging techniques, where we show that they contain a high density of defects, leading to nonstoichiometric single crystals of both semimetals. Despite the observed defects and nonstoichiometry on samples grown using techniques already reported in the literature, de Haas-van Alphen measurements on TaP reveal quantum oscillations and a high carrier mobility, an indication that the crystals are of... Show moreWe report a structural study of the Weyl semimetals TaAs and TaP, utilizing diffraction and imaging techniques, where we show that they contain a high density of defects, leading to nonstoichiometric single crystals of both semimetals. Despite the observed defects and nonstoichiometry on samples grown using techniques already reported in the literature, de Haas-van Alphen measurements on TaP reveal quantum oscillations and a high carrier mobility, an indication that the crystals are of quality comparable to those reported elsewhere. Electronic structure calculations on TaAs reveal that the position of the Weyl points relative to the Fermi level shift with the introduction of vacancies and stacking faults. In the case of vacancies the Fermi surface becomes considerably altered, while the effect of stacking faults on the electronic structure is to allow the Weyl pockets to remain close to the Fermi surface. The observation of quantum oscillations in a nonstoichiometric crystal and the persistence of Weyl fermion pockets near the Fermi surface in a crystal with stacking faults point to the robustness of these quantum phenomena in these materials. Show less

Date Issued

2016-06-27

Identifier

FSU_libsubv1_wos_000378816000007, 10.1103/PhysRevB.93.245152

Format

Citation

Title

Chiral spin liquid from magnetic Wannier states.

Creator

Panfilov, I., Patri, A., Yang, Kun, Burkov, A. A.

Abstract/Description

We present a mapping of a two-dimensional system of interacting bosons in a strong perpendicular magnetic field to an equivalent system of interacting bosons on the square lattice in the absence of the field. The mapping utilizes a magnetic Bloch and the corresponding magnetic Wannier single-particle basis in the lowest Landau level. By construction, the ground states of the resulting model of interacting bosons on the square lattice are gapped fractionalized liquids or gapless Bose metal... Show moreWe present a mapping of a two-dimensional system of interacting bosons in a strong perpendicular magnetic field to an equivalent system of interacting bosons on the square lattice in the absence of the field. The mapping utilizes a magnetic Bloch and the corresponding magnetic Wannier single-particle basis in the lowest Landau level. By construction, the ground states of the resulting model of interacting bosons on the square lattice are gapped fractionalized liquids or gapless Bose metal states with broken time-reversal symmetry at specific rational filling fractions. Show less

We report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P (4) over bar2(1)m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4, Ce2IrAl7Ge4, and Ce2NiAl7Ge4 order... Show moreWe report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P (4) over bar2(1)m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4, Ce2IrAl7Ge4, and Ce2NiAl7Ge4 order magnetically below T-M = 1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. The small amount of entropy released in the magnetic state of Ce2MAl7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point. Show less

Several technical issues and challenges are identified and investigated for the planar tunneling spectroscopy of the topological Kondo insulator SmB6. Contrasting behaviors of the tunnel junctions prepared in two different ways are analyzed and explained in detail. The conventional approach based on an AlOx tunnel barrier results in unsatisfactory results due to the interdiffusion between SmB6 and deposited Al. On the contrary, plasma oxidation of SmB6 crystals produces high-quality tunnel... Show moreSeveral technical issues and challenges are identified and investigated for the planar tunneling spectroscopy of the topological Kondo insulator SmB6. Contrasting behaviors of the tunnel junctions prepared in two different ways are analyzed and explained in detail. The conventional approach based on an AlOx tunnel barrier results in unsatisfactory results due to the interdiffusion between SmB6 and deposited Al. On the contrary, plasma oxidation of SmB6 crystals produces high-quality tunnel barriers on both (001) and (011) surfaces. Resultant conductance spectra are highly reproducible with clear signatures for the predicted surface Dirac fermions and the bulk hybridization gap as well. The surface states are identified to reside on two or one distinguishable Dirac cone(s) on the (001) and (011) surface, respectively, in good agreement with the recent literature. However, their topological protection is found to be limited within the low energy region due to their inevitable interaction with the bulk excitations, called spin excitons, consistent with a recent theoretical prediction. Implications of our findings on other physical properties in SmB6 and also other correlated topological materials are remarked. Show less

Date Issued

2017-05-15

Identifier

FSU_libsubv1_wos_000401449700001, 10.1103/PhysRevB.95.195129

Format

Citation

Title

Phase separation and superparamagnetism in the martensitic phase of Ni50-xCoxMn40Sn10.

Ni50-xCoxMn40Sn10 shape memory alloys in the approximate range 5
Show moreNi50-xCoxMn40Sn10 shape memory alloys in the approximate range 5 <= x <= 8 display desirable properties for applications as well as intriguing magnetism. These off-stoichiometric Heusler alloys undergo a martensitic phase transformation at a temperature T-M of 300-400 K, from ferromagnetic (FM) to nonferromagnetic, with unusually low thermal hysteresis and a large change in magnetization. The low temperature magnetic structures in the martensitic phase of such alloys, which are distinctly inhomogeneous, are of great interest but are not well understood. Our present use of spin echo nuclear magnetic resonance in the large hyperfine fields at Mn-55 sites provides compelling evidence that nanoscale magnetic phase separation into FM and antiferromagnetic (AFM) regions occurs below T-M in alloys with x in the range 0 to 7. At finite Co substitution, the FM regions are found to be of two distinct types, corresponding to high and low local concentrations of Co on Ni sites. Estimates of the size distributions of both the FM and AFM nanoregions have been made. At x = 7, the AFM component is not long-range ordered, even below 4 K, and is quite different from the AFM component found at x = 0; by x = 14, the FM phase is completely dominant. Of particular interest, we find for x = 7 that field cooling leads to dramatic changes in the AFM regions. These findings provide insight into the origins of magnetic phase separation and superparamagnetism in these complex alloys, particularly their intrinsic exchange bias, which is of considerable current interest. Show less

Date Issued

2016-03-21

Identifier

FSU_libsubv1_wos_000372711200004, 10.1103/PhysRevB.93.094425

Format

Citation

Title

Peculiarities of superconductivity in the single-layer FeSe/SrTiO3 interface.

Creator

Gor'kov, Lev P.

Abstract/Description

Observation of replica bands in the angle-resolved photoemission spectroscopy (ARPES) spectra of single-layer FeSe on a strontium titanate substrate revealed a phonon component contribution to mechanisms behind its high-T-c superconductivity. We study the interaction of the in-layer FeSe electrons with the electric potential of the longitudinal (LO) modes at the surface of bulk SrTiO3. A two-dimensional system of charges at the FeSe/SrTiO3 interface includes both the itinerant and the... Show moreObservation of replica bands in the angle-resolved photoemission spectroscopy (ARPES) spectra of single-layer FeSe on a strontium titanate substrate revealed a phonon component contribution to mechanisms behind its high-T-c superconductivity. We study the interaction of the in-layer FeSe electrons with the electric potential of the longitudinal (LO) modes at the surface of bulk SrTiO3. A two-dimensional system of charges at the FeSe/SrTiO3 interface includes both the itinerant and the immobile electrons. The latter significantly change the interface characteristics, increasing screening at the substrate surface and thereby reducing the strength of the electron-LO-phonon interaction. In what follows, the dielectric constant serves as a free parameter and is determined using the ARPES measurements of the replicas. Two-dimensional Coulomb screening is accounted for in the random-phase approximation. It is shown that the model is applicable over the entire range of the parameters typical for current experiments. The estimates from this model make possible the conclusion that the LO-phonon-mediated pairing alone cannot account for the temperatures of the superconducting transitions T-c in the single-layer FeSe/SrTiO3 reported in these experiments. This does not exclude that the LO-phonon mechanisms can become more significant in differently and better prepared single-layer FeSe films. Available experiments are briefly discussed. Thus far no measurements exist on the dependence of T-c on the concentration of electrons doped into the in-layer FeSe band. Show less

Date Issued

2016-02-12

Identifier

FSU_libsubv1_wos_000370021500003, 10.1103/PhysRevB.93.060507

Format

Citation

Title

Persistence Of Slow Fluctuations In The Overdoped Regime Of Ba(fe1-xrhx)(2)as-2 Superconductors.

We present nuclear magnetic resonance evidence that very slow (
Show moreWe present nuclear magnetic resonance evidence that very slow (<= 1 MHz) spin fluctuations persist into the overdoped regime of Ba(Fe1-xRhx)(2)As-2 superconductors. Measurements of the As-75 spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating (pi/a, 0) from (0, pi/a) correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime. Show less

By using Gutzwiller projected fermionic wave functions and variational Monte Carlo technique, we study the spin-1/2 Heisenberg model with the first-neighbor (J(1)), second-neighbor (J(2)), and additional scalar chiral interaction J(chi)S(i) . (S-j x S-k) on the triangular lattice. In the nonmagnetic phase of the J(1)-J(2) triangular model with 0.08 less than or similar to J(2)/J(1) less than or similar to 0.16, recent density-matrix renormalization group (DMRG) studies [Zhu and White, Phys.... Show moreBy using Gutzwiller projected fermionic wave functions and variational Monte Carlo technique, we study the spin-1/2 Heisenberg model with the first-neighbor (J(1)), second-neighbor (J(2)), and additional scalar chiral interaction J(chi)S(i) . (S-j x S-k) on the triangular lattice. In the nonmagnetic phase of the J(1)-J(2) triangular model with 0.08 less than or similar to J(2)/J(1) less than or similar to 0.16, recent density-matrix renormalization group (DMRG) studies [Zhu and White, Phys. Rev. B 92, 041105(R) (2015) and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403(R) (2015)] find a possible gapped spin liquid with the signal of a competition between a chiral and a Z(2) spin liquid. Motivated by the DMRG results, we consider the chiral interaction J(chi)S(i) . (S-j x S-k) as a perturbation for this nonmagnetic phase. We find that with growing J(chi), the gapless U(1) Dirac spin liquid, which has the best variational energy for J(chi) = 0, exhibits the energy instability towards a gapped spin liquid with nontrivial magnetic fluxes and nonzero chiral order. We calculate topological Chern number and ground-state degeneracy, both of which identify this flux state as the chiral spin liquid with fractionalized Chern number C = 1/2 and twofold topological degeneracy. Our results indicate a positive direction to stabilize a chiral spin liquid near the nonmagnetic phase of the J(1)-J(2) triangular model. Show less

Date Issued

2016-08-15

Identifier

FSU_libsubv1_wos_000381482600002, 10.1103/PhysRevB.94.075131

Format

Citation

Title

Wiedemann-Franz law in the underdoped cuprate superconductor YBa2Cu3Oy.

The electrical and thermal Hall conductivities of the cuprate superconductor YBa2Cu3Oy, sigma(xy) and kappa(xy), were measured in a magnetic field up to 35 T, at a hole concentration (doping) p = 0.11. In the T = 0 limit, we find that the Wiedemann-Franz law, kappa(xy)/T = (pi(2)/3)(k(B)/e)(2)sigma(xy), is satisfied for fields immediately above the vortex-melting field H-vs. This rules out the existence of a vortex liquid at T = 0 and it puts a clear constraint on the nature of the normal... Show moreThe electrical and thermal Hall conductivities of the cuprate superconductor YBa2Cu3Oy, sigma(xy) and kappa(xy), were measured in a magnetic field up to 35 T, at a hole concentration (doping) p = 0.11. In the T = 0 limit, we find that the Wiedemann-Franz law, kappa(xy)/T = (pi(2)/3)(k(B)/e)(2)sigma(xy), is satisfied for fields immediately above the vortex-melting field H-vs. This rules out the existence of a vortex liquid at T = 0 and it puts a clear constraint on the nature of the normal state in underdoped cuprates, in a region of the doping phase diagram where charge-density-wave order is known to exist. As the temperature is raised, the Lorenz ratio, L-xy = kappa(xy)/(sigma T-xy), decreases rapidly, indicating that strong small-q scattering processes are involved. Show less

The temperature- (T) magnetic-field (H) phase diagram for the tetragonal layered compound CeSbSe is determined from magnetization, specific heat, and electrical resistivity measurements. This system exhibits complex magnetic ordering at T-M = 3 K and the application of a magnetic field results in a cascade of magnetically ordered states for H less than or similar to 1.8 T which are characterized by fractional integer size steps: i.e., a possible devil's staircase is observed. Electrical... Show moreThe temperature- (T) magnetic-field (H) phase diagram for the tetragonal layered compound CeSbSe is determined from magnetization, specific heat, and electrical resistivity measurements. This system exhibits complex magnetic ordering at T-M = 3 K and the application of a magnetic field results in a cascade of magnetically ordered states for H less than or similar to 1.8 T which are characterized by fractional integer size steps: i.e., a possible devil's staircase is observed. Electrical transport measurements show a weak temperature dependence and large residual resistivity which suggest a small charge-carrier density and strong scattering from the f moments. These features reveal Kondo lattice behavior where the f moments are screened incompletely, resulting in a fine balanced magnetic interaction between different Ce neighbors that is mediated by the Ruderman-Kittel-Kasuya-Yosida interaction. This produces the nearly degenerate magnetically ordered states that are accessed under an applied magnetic field. Show less

Date Issued

2017-07-17

Identifier

FSU_libsubv1_wos_000405697200002, 10.1103/PhysRevB.96.014421

Format

Citation

Title

Possible Nematic Spin Liquid In Spin-1 Antiferromagnetic System On The Square Lattice: Implications For The Nematic Paramagnetic State Of Fese.

Creator

Gong, Shou-Shu, Zhu, W., Sheng, D. N., Yang, Kun

Abstract/Description

The exotic normal state of iron chalcogenide superconductor FeSe, which exhibits vanishing magnetic order and possesses an electronic nematic order, triggered extensive explorations of its magnetic ground state. To understand its novel properties, we study the ground state of a highly frustrated spin-1 system with bilinear-biquadratic interactions using an unbiased large-scale density matrix renormalization group. Remarkably, with increasing biquadratic interactions, we find a paramagnetic... Show moreThe exotic normal state of iron chalcogenide superconductor FeSe, which exhibits vanishing magnetic order and possesses an electronic nematic order, triggered extensive explorations of its magnetic ground state. To understand its novel properties, we study the ground state of a highly frustrated spin-1 system with bilinear-biquadratic interactions using an unbiased large-scale density matrix renormalization group. Remarkably, with increasing biquadratic interactions, we find a paramagnetic phase between Neel and stripe magnetic ordered phases. We identify this phase as a candidate of nematic quantum spin liquid by the compelling evidences, including vanished spin and quadrupolar orders, absence of lattice translational symmetry breaking, and a persistent nonzero lattice nematic order in the thermodynamic limit. The established quantum phase diagram naturally explains the observations of enhanced spin fluctuations of FeSe in neutron scattering measurement and the phase transition with increasing pressure. This identified paramagnetic phase provides a possibility to understand the novel properties of FeSe. Show less

Date Issued

2017-05-19

Identifier

FSU_libsubv1_wos_000401654300004, 10.1103/PhysRevB.95.205132

Format

Citation

Title

Probing The Magnetic Field Dependence Of The Light Hole Transition In Gaas/algaas Quantum Wells Using Optically Pumped Nmr.

Optically pumped NMR (OPNMR) of the NMR-active Ga-69/71 species has been shown to be a unique method to probe electronic energy bands in GaAs, with sensitivity to the light hole-to-conduction band transition. This transition is often obscured in other optical measurements such as magnetoabsorption. Using OPNMR, we exploit the hyperfine interaction between conduction band electrons (and their spin states) and nuclear spins, which are detected through phase-sensitive radio-frequency (NMR)... Show moreOptically pumped NMR (OPNMR) of the NMR-active Ga-69/71 species has been shown to be a unique method to probe electronic energy bands in GaAs, with sensitivity to the light hole-to-conduction band transition. This transition is often obscured in other optical measurements such as magnetoabsorption. Using OPNMR, we exploit the hyperfine interaction between conduction band electrons (and their spin states) and nuclear spins, which are detected through phase-sensitive radio-frequency (NMR) spectroscopy. Measurements were made over a range of external magnetic fields (B-0) in two different labs with separate experimental setups to obtain the magnetic field dependence of the light hole-to-conduction band transition energy. In addition, k . p theory was used to interpret the experimental results, mapping out this specific transition's magnetic field dependence in an AlGaAs/GaAs quantum well. The combination of theory and experiment point to a mixing of valence bands at a field of approximately B-0 = 4.7 T, swapping the dominant character of the absorption transition and, thus, explaining the magnetic field dependence. Lastly, the experimental dependence of the light hole-to-conduction band transition energy on B-0 is found to be less steep compared to the calculated trend, indicating that inclusion of additional effects may be necessary to accurately model the spin-split band structure. The additional insight gained by Ga-69/71 OPNMR about the light hole states will facilitate future testing of more complex band structure models. Show less

A codimension-one critical surface in momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the noninteracting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. The presence of such surfaces gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real-space... Show moreA codimension-one critical surface in momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the noninteracting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. The presence of such surfaces gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real-space entanglement entropy. The fundamental difference between a Fermi surface and a Bose surface is revealed by the fact that the logarithmic terms in entanglement entropies differ by a factor of 2: S-log(Bose) = 2S(log)(Fermi), even when they have identical geometry. Our method has remarkable similarity with determining Fermi surface shape using quantum oscillation. We also discuss possible probes of concave critical surfaces in momentum space. Show less

Date Issued

2016-03-23

Identifier

FSU_libsubv1_wos_000372716500001, 10.1103/PhysRevB.93.121109

Format

Citation

Title

Search For A Nematic Phase In The Quasi-two-dimensional Antiferromagnet Cucro2 By Nmr In An Electric Field.

The magnetic phase diagram of CuCrO2 was studied with an alternative method of simultaneous Cu NMR and electric polarization techniques with the primary goal of demonstrating that, regardless of cooling history of the sample, the magnetic phase with specific helmet-shaped NMR spectra associated with interplanar disorder possesses electric polarization. Our result unequivocally confirms the assumption of Sakhratov et al. [Phys. Rev. B 94, 094410 ( 2016)] that the high-field low-temperature... Show moreThe magnetic phase diagram of CuCrO2 was studied with an alternative method of simultaneous Cu NMR and electric polarization techniques with the primary goal of demonstrating that, regardless of cooling history of the sample, the magnetic phase with specific helmet-shaped NMR spectra associated with interplanar disorder possesses electric polarization. Our result unequivocally confirms the assumption of Sakhratov et al. [Phys. Rev. B 94, 094410 ( 2016)] that the high-field low-temperature phase is in fact a three-dimensional (3D) polar phase characterized by a 3D magnetic order with tensor order parameter. In comparison with the results obtained in pulsed fields, a modified phase diagram is introduced defining the upper boundary of the first-order transition from the 3D spiral to the 3D polar phase. Show less

The orthorhombic perovskite SrIrO3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal Sr0.94Ir0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIrO3. It retains the same crystal structure as stoichiometric SrIrO3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring... Show moreThe orthorhombic perovskite SrIrO3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal Sr0.94Ir0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIrO3. It retains the same crystal structure as stoichiometric SrIrO3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear temperature dependence up to 800 K but the strong electronic anisotropy renders an insulating behavior in the out-of-plane resistivity. The Hall resistivity undergoes an abrupt sign change and grows below 40 K, which along with the Sommerfeld constant of 20 mJ/mol K-2 suggests a multiband effect. All results including our first-principles calculations underscore a delicacy of the paramagnetic, metallic state in SrIrO3 that is in close proximity to an AFM insulating state. The contrasting ground states in isostructural Sr0.94Ir0.78O2.68 and SrIrO3 illustrate a critical role of lattice distortions and Ir deficiency in rebalancing the ground state in the iridates. Finally, the concurrent AFM and MI transitions reveal a direct correlation between the magnetic transition and formation of an activation gap in the iridate, which is conspicuously absent in Sr2IrO4. Show less

We analyze the properties of a non-Abelian spin-one chiral spin liquid state proposed by Greiter and Thomale [Phys. Rev. Lett. 102, 207203 (2009)] using Monte Carlo. In this state the bosonic nu = 1 Moore-Read Pfaffian wave function is used to describe a gas of bosonic spin flips on a square lattice with one flux quantum per plaquette. For toroidal geometries there is a three-dimensional space of these states corresponding to the topological degeneracy of the bosonic Moore-Read state on the... Show moreWe analyze the properties of a non-Abelian spin-one chiral spin liquid state proposed by Greiter and Thomale [Phys. Rev. Lett. 102, 207203 (2009)] using Monte Carlo. In this state the bosonic nu = 1 Moore-Read Pfaffian wave function is used to describe a gas of bosonic spin flips on a square lattice with one flux quantum per plaquette. For toroidal geometries there is a three-dimensional space of these states corresponding to the topological degeneracy of the bosonic Moore-Read state on the torus. We show that spin correlations for different states in this space become indistinguishable for large system size. We also calculate the Renyi entanglement entropy for different system partitions to extract the topological entanglement entropy and provide evidence that the topological order of the lattice spin-liquid state is the same as that of the continuum Moore-Read state from which it is constructed. Show less

A coordinated study on electrochemical, magnetic, optical, and transport properties of poly(1, 4- dimethoxy phenylene vinylene) (PDMPV) using in situ electrochemical doping techniques is presented. Properties are correlated through a common axis of applied voltage. Electrochemical doping shows approx. 100% Coulombic efficiency up to an applied potential of 3.8 V versus lithium in propylene carbonate electrolyte. Conductivity increases in a reversible manner to a maximum of 250 0 ' cm ' and an... Show moreA coordinated study on electrochemical, magnetic, optical, and transport properties of poly(1, 4- dimethoxy phenylene vinylene) (PDMPV) using in situ electrochemical doping techniques is presented. Properties are correlated through a common axis of applied voltage. Electrochemical doping shows approx. 100% Coulombic efficiency up to an applied potential of 3.8 V versus lithium in propylene carbonate electrolyte. Conductivity increases in a reversible manner to a maximum of 250 0 ' cm ' and an applied potential of 3.9 V. Potentials in excess of 3.9 V cause an irreversible decrease in conductivity. Spin and charge show a 1:1 relation on/y to very low doping levels. Two paramagnetic species are produced on doping. A maximum spin concentration is observed at =3.7 V. The ultraviolet —visible —near-infrared spectra of doped PDMPV show at least five absorption bands, at 4.8, 3.7, 2.5, 1.7, and 0.6 eV. The first three bands decrease with doping and the latter two increase. When analyzed by the polaron or bipolaron model, the optical data imply significant symmetry breaking, Contributions to the optical activity from polarons and bipolarons are determined from the EPR results and are found to be di6'erent for both peaks, implying greater symmetrybreaking eA'ects for polarons. An electrochemical analysis of EPR results suggests that polaron interaction energies are =0.4S eV greater than those for bipolarons. Show less

Date Issued

1989

Identifier

FSU_migr_chm_faculty_publications-0006

Format

Citation

Title

Thermodynamic Constraints On The Amplitude Of Quantum Oscillations.

Creator

Shekhter, Arkady, Modic, K. A., McDonald, R. D., Ramshaw, B. J.

Abstract/Description

Magneto-quantum oscillation experiments in high-temperature superconductors show a strong thermally induced suppression of the oscillation amplitude approaching the critical dopings [B.J. Ramshaw et al., Science 348, 317 (2014); H. Shishido et al., Phys. Rev. Lett. 104, 057008 (2010); P. Walmsley et al., Phys. Rev. Lett. 110, 257002 (2013)]-in support of a quantum-critical origin of their phase diagrams. We suggest that, in addition to a thermodynamic mass enhancement, these experiments may... Show moreMagneto-quantum oscillation experiments in high-temperature superconductors show a strong thermally induced suppression of the oscillation amplitude approaching the critical dopings [B.J. Ramshaw et al., Science 348, 317 (2014); H. Shishido et al., Phys. Rev. Lett. 104, 057008 (2010); P. Walmsley et al., Phys. Rev. Lett. 110, 257002 (2013)]-in support of a quantum-critical origin of their phase diagrams. We suggest that, in addition to a thermodynamic mass enhancement, these experiments may directly indicate the increasing role of quantum fluctuations that suppress the quantum oscillation amplitude through inelastic scattering. We show that the traditional theoretical approaches beyond Lifshitz-Kosevich to calculate the oscillation amplitude in correlated metals result in a contradiction with the third law of thermodynamics and suggest a way to rectify this problem. Show less

We report thickness-tuned electrical transport in highly anisotropic three-dimensional Dirac semimetal ZrTe5 nanosheets with thickness down to 10 nm. We find that the resistivity peak temperature T* can be significantly tuned by the nanosheet thickness. When the thickness is reduced from 160 to 40 nm, T* reduces systematically from 145 to 100 K. However, with the thickness further reducing to 10 nm, T* shifts up to a higher temperature. From our analysis, the system transitions from a... Show moreWe report thickness-tuned electrical transport in highly anisotropic three-dimensional Dirac semimetal ZrTe5 nanosheets with thickness down to 10 nm. We find that the resistivity peak temperature T* can be significantly tuned by the nanosheet thickness. When the thickness is reduced from 160 to 40 nm, T* reduces systematically from 145 to 100 K. However, with the thickness further reducing to 10 nm, T* shifts up to a higher temperature. From our analysis, the system transitions from a topological semimetal with two types of carriers to a single band with conventional hole carriers when the thickness is less than 40 nm. Furthermore, by tracking the thickness dependence of the carrier density, we find that the Fermi level shifts continuously downward from the conduction band to the valence band with decreasing the thickness. Our experiment reveals a thickness-tuned transition of band topology in ZrTe5 nanosheets which may be helpful for the understanding of the contrast observations in this material. Show less

Date Issued

2017-03-29

Identifier

FSU_libsubv1_wos_000399142500003, 10.1103/PhysRevB.95.125135

Format

Citation

Title

Transport evidence for the three-dimensional Dirac semimetal phase in ZrTe5.

Topological Dirac semimetal is a newly discovered class of materials which has attracted intense attention. This material can be viewed as a three-dimensional (3D) analog of graphene and has linear energy dispersion in bulk, leading to a range of exotic transport properties. Here we report direct quantum transport evidence of the 3D Dirac semimetal phase of layered material ZrTe5 by angular-dependent magnetoresistance measurements under high magnetic fields up to 31 T. We observed very clear... Show moreTopological Dirac semimetal is a newly discovered class of materials which has attracted intense attention. This material can be viewed as a three-dimensional (3D) analog of graphene and has linear energy dispersion in bulk, leading to a range of exotic transport properties. Here we report direct quantum transport evidence of the 3D Dirac semimetal phase of layered material ZrTe5 by angular-dependent magnetoresistance measurements under high magnetic fields up to 31 T. We observed very clear negative longitudinal magnetoresistance induced by chiral anomaly under the condition of the magnetic field aligned only along the current direction. Pronounced Shubnikov-de Hass (SdH) quantum oscillations in both longitudinal magnetoresistance and transverse Hall resistance were observed, revealing anisotropic light cyclotron masses and high mobility of the system. In particular, a nontrivial pi-Berry phase in the SdH oscillations gives clear evidence for the 3D Dirac semimetal phase. Furthermore, we observed clear Landau level splitting under high magnetic field, suggesting possible splitting of the Dirac point into Weyl points due to broken time-reversal symmetry. Our results indicate that ZrTe5 is an ideal platform to study 3D massless Dirac and Weyl fermions in a layered compound. Show less